Malaysia Airlines Flight MH370 search shows extent of ocean trash

Search teams scouring the Indian Ocean for pieces of the missing Malaysia Airlines plane thought they had promising clues earlier this week.

Turns out, they were only finding bits of abandoned fishing equipment.

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Last week, a French satelliteidentified an apparent debris field containing 122 objects. That, too, was inconclusive.

These false leads are not only heartbreaking for the families of those who were on board the missing airliner MH370, but give an indication of the vast amount of junk floating in the open seas.

"Basically, the world's oceans are plasticized," says Marcus Eriksen, executive director of the 5 Gyres Institute, a conservation group that researches the amount of plastic pollution in the planet's seas.

Because of the difficulty of measuring, there are varying estimates of just how much trash is in our oceans.

Oceanographer Charles Moore, who works with the Algalita Marine Research Institute in Long Beach, Calif., estimates there could be 200 million tonnes of plastic debris floating in the seas. This calculation is based on the belief that 2.5 per cent of the world's plastic lands in the ocean.

Eriksen says there are currently no reliable estimates of the amount of ocean junk worldwide, and he is hoping that a coming report by 5 Gyres will be the first reliable global estimate.

It's based on 24 expeditions over the course of six years by six colleagues, and it found that there are nearly 5.25 trillion particles of plastic trash in the oceans, weighing half a million tonnes.

"You're going to find some lightbulbs, fluorescent tubes, some wood, some coconuts and seeds, but by and large, it's mostly plastic," says Eriksen.

These estimates don't include the detritus that's sitting at the bottom of the oceans, which, as he says, is "virtually unknown."

'Deathtraps for marine animals'

One major constituent of ocean junk is fishing gear such as nets and buoys, says Eric Galbraith, an assistant professor in the department of earth and planetary science at McGill University.

"Floating nets often come adrift, and cause particularly bad problems because they can be long-lived deathtraps for marine animals," he says.

The garbage found at sea comes from a variety of sources. Some of it is deposited in rivers that empty into larger bodies of water, while some is drawn into the ocean during natural disasters like tsunamis.

This debris is pushed around by ocean currents. While trash can be found all over the high seas, it has become especially prominent in the five gyres -- large systems of rotating ocean currents that exist between the continents.

They include the North Atlantic and South Atlantic gyres, the North Pacific and South Pacific gyres and the Indian Ocean gyre, which is just west of the area where the Malaysia Airlines plane is thought to have gone down.

Due to global wind patterns, air continually pushes the surface water of the gyres, and the plastic in it, towards the centres of the ocean basin. But since plastic floats, it just continually returns to the top, and remains more or less in place.

"The gyres concentrate the garbage at the surface, just like a filter in a bathtub drain concentrates the hairs from a bath," says Galbraith.

The most infamous example of this is what's known as the Great Pacific Garbage Patch. Located between Hawaii and California in the middle of the North Pacific gyre, it was first described by Charles Moore in an article for Natural History magazine in 1993.

In photographs, it's a roiling soup of plastic bottles, caps, wrappers and other disposable goods. According to National Geographic magazine, scientists have gathered up to 750,000 bits of plastic in a square kilometre of that patch.

Taking out the trash

A great deal of garbage is also dumped directly into the oceans by cruise and cargo ships.

The United Nations Convention on the Law of the Sea (1982) encourages nations to take "all measures necessary to prevent, reduce, and control pollution of the marine environment from any source."

Galbraith says that for a long time, there was a general understanding that unless it was chemical waste, it was fine to toss junk from ships into international waters.

There are now stricter rules in place. In 2012, the International Maritime Organization adopted measures to prohibit the disposal of plastics anywhere in the sea. "But it takes time to change old habits," says Galbraith.

There is also the problem of accidental garbage, like when turbulent weather blows shipping containers overboard, which led to the famous release of 29,000 plastic ducks in the Pacific Ocean in January 1992.

The World Shipping Council says about 350 containers are lost at sea each year, although non-industry observers estimate the annual rate to be much higher.

"There are a lot of container ships that carry material goods all over the planet, and it turns out that it's cheaper to allow a certain amount of loss off those ships than it is to make sure that they're absolutely storm-proof," says Galbraith.

While there has been international debate about how to clean up the trash-strewn corners of the sea, Eriksen says that the very nature of the plastic problem makes it almost impossible.

It's been estimated that 93 per cent of those plastic particles bobbing in the seas are about the size of a grain of rice or smaller.

"That really makes clean-up very impractical," says Eriksen. "You can't get all these trillions of small particles out of the ocean."